The invention relates to a detecting method, and more particularly to a method of detecting an array of a liquid crystal display.
Conventionally, a defect in an array of a liquid crystal display (for example, a thin film transistor liquid crystal display, TFT LCD) is detected by contact detection (for example, probe detection) or non-contact detection (for example, electron beam or optical detection). FIG. 1 shows a pixel P1 of an array of a TFT LCD detected by an electron beam, wherein pixel P1 comprises a transparent electrode D1, a thin film transistor T1 and a capacitance C1. In electron beam detection, a voltage is applied to transparent electrode D1, and an electron source 11 emits an electron beam toward transparent electrode D1. The electron beam is generated by transparent electrode D1 and produces secondary electrons. Secondary electrons are received by a sensor 12. An array defect (for example, a data line break or a short between a transparent electrode and a data line) increases positive or negative electric charges on transparent electrode D1, and changes a quantity of secondary electrons received by sensor 12 (due to repulsion between same charges and attraction between different charges). Thus, array defects are detected by examining the quantity of secondary electrons received by sensor 12.
Conventional detection methods, however, cannot completely detect all defects of a thin film transistor, such as high-temperature defects (defect revealed only at high temperature, for example, “TFT weak”). The term “TFT weak” is described here after. FIG. 2 shows performance curves of thin film transistors. Dotted curve 20 is a performance curve of an ideal thin film transistor. Under ideal circumstances, when a current input is lower than a threshold voltage, current flux of the thin film transistor is low, and a light path in a liquid crystal layer (not shown) is closed. When current input is higher than a threshold voltage, current flux of the thin film transistor is increased, and light path in the liquid crystal layer is open. Curve 21 is a performance curve of a normal thin film transistor. Normal circumstances are similar to ideal circumstances, wherein the light path in the liquid crystal layer is opened only when current input is higher than threshold voltage. Curve 22 is a performance curve of a weak thin film transistor which leaks current when temperature thereof increases, wherein current flux of the thin film transistor is too high when current input is lower than threshold voltage. In normal white mode, a weak TFT constantly opens light path, and the liquid crystal display shows bright point(s) (bright point defect) when displaying an all-black image. In normal black mode, a weak TFT constantly closes the light path, and liquid crystal display shows a dark point (black point defect) when displaying an all-white image.
When a liquid crystal display operates, a backlight module thereof heats the liquid crystal display array. Thus, if a high-temperature defect exists in the TFT, bright point defects or black point defects are revealed. Conventional array detection is performed directly after an array process without being exposed to heat. Thus, high-temperature defects cannot be found by conventional detection. In practice, high-temperature defects are conventionally discovered after a cell process and a backlight module packing process, and the cost of reworking or nullifying defective liquid crystal displays is quite high.